$opts = array(
        "--start",$create_timestamp,
        "--step","300",
        "DS:linktimeout:COUNTER:600:0:100",
        "DS:airdelay:COUNTER:600:0:1000",
        "DS:sessioncount:COUNTER:600:0:10000",
        "DS:regcount:COUNTER:600:0:1000",
        "DS:reregcount:COUNTER:600:0:1000",
        "DS:rssi:GAUGE:600:0:2000",
        "DS:lastrssi:GAUGE:600:0:2000",
        "DS:averagejitter:GAUGE:600:0:20",
        "DS:lastjitter:GAUGE:600:0:20",
        "DS:averagepowerlevel:GAUGE:600:-120:0",
        "DS:lastpowerlevel:GAUGE:600:-120:0",
        "RRA:AVERAGE:0.5:1:24",
        "RRA:AVERAGE:0.5:6:10",
      );

Update:

    $update_body = 
      // $timestamp . ":" . 
      "N:" .      
      $this->returnLinktimeout(). ":" .
      $this->returnAirdelay(). ":" .
      $this->returnSessioncount(). ":" .
      $this->returnRegcount(). ":" .
      $this->returnReregcount(). ":" .
      $this->returnRssi(). ":" .
      $this->returnLastrssi(). ":" .
      $this->returnAveragejitter(). ":" .
      $this->returnLastjitter(). ":" .
      $this->returnAveragepowerlevel(). ":" .
      $this->returnLastpowerlevel();

    echo $update_body . " ";
    $ret = rrd_update($rrd_filename, $update_body);